Mike,
One more detail in case it makes any difference:
I just remembered upon looking at my turntable base: As I said, I have the Maple Block (on which the turntable sits), sitting atop the stainless steel sheet, and then beneath that, the two layer sandwich of MDF held up by the pods.
I actually undercut the size of the steel/MDF beneath the maple block so the maple block overhangs the rest by around an inch or so. The reason is, the Maple block is the pretty part of the whole thing and I wanted it just floating with the turntable above it. MDF isn't exactly beautiful. So in cutting it inset about an inch under the maple block, and painting the MDF and stainless steel with matte black paint, they completely disappear from view under the shadow of the maple block. So all you see above the rack, sort of floating, is the maple block and turntable.
So actually, not too long after painting the steel on both sides with the paint (it was dry), the paint also provided something of a bond-like friction to both the maple block above it, and the MDF below it.